Yan 

You seem to think that simply keeping the brakes constantly applied will always result in a large amount of heat to be generated. Causing the drag braking technique to always out-heat the pulse technique. "Because it never has a chance to cool".

The gap in your science knowledge is in not understanding that the amount of heat is not solely based on brake on vs brake off, but also related to how hard the brake is being applied when it IS on. In middle school or high school physics you should have been taught, assuming your state's curriculum is similar to that of other regions, that frictional force = coefficient of friction x normal force. The important factor here is the normal force. If you keep the normal force very small, the friction force will also be very small. That means the amount of heat generated will be very small.

Here the question is not "but why would a rider only drag brake by 0.5 mph?" The question is, "what would happen if he simply chooses to do it?" The answer is that the heat put into the rims would be very small, with the graph eventually converging on zero as the normal force is infinitely reduced.

It should be obvious to most people by now that drag vs pulse braking is not the determining factor on how much heat is retained in the rim. You can drag brake in a way that ends with cooler rims, just as you can pulse in a way that ends in cooler rims. The rider's action determines the temperature result, it is not fixed to "drag always hotter no matter what".

I apologize for being sarcastic in my previous post, but until you catch up on this part of basic physics, you're simply not going to understand how this works. Maybe give that book another read. Not sure if this is covered or if he just assumes you already know. Good luck!